"I regard the brain as a computer which will stop working when its components fail. There is no heaven or afterlife for broken down computers; that is a fairy story for people afraid of the dark." ~ Stephen Hawking

There are too many good ones to pick a single favorite, but here is one that I enjoyed.

"I'm sorry, but that's completely ridiculous! How can I possibly prove it doesn't exist? I mean you could claim that anything's real if the only basis for believing in it is that nobody's proved it doesn't exist." ~ Hermione Granger

by ascribing it to his gods... When, therefore, he ascribes to his gods the production of some phenomenon... does he, in fact, do any thing more than substitute for the darkness of his own mind, a sound to which he has been accustomed to listen with reverential awe?